Polyvalent unsaturated fatty acids such as DHA, DPA, EPA and ARA have been known to be contained richly as a fat or oil in fish such as tuna, yellowtail, mackerel, eel or sardine, an animal living in the sea such as seal, or a microorganism. These polyvalent unsaturated fatty acids, for instance, exhibit various physiological activities such as action for suppressing platelet aggregation, action for lowering neutral lipid in blood, action for ameliorating learning and memorization and action for ameliorating allergy.
However, these polyvalent unsaturated fatty acids are very highly likely to be oxidized, so that the deterioration of the tastes takes place, so that unpleasant odor and taste are exhibited in some cases. Therefore, in a case where a fish oil is utilized as food, various methods of preventing generation of unpleasant odors and oxidization have been proposed.
As the methods, there have been known, for instance, a method of coating a fish oil with a protein hydrolysate and a milk solid content (see, for instance, Japanese Patent Laid-Open No. Hei 5-98286), a method of blending a fish oil in a powdered milk for infant rearing (see, for instance, Japanese Patent Laid-Open No. Hei 1-80250), a method of wrapping a fish oil with cyclodextrin (see, for instance, Japanese Patent Laid-Open No. Hei 4-178348), a method of improving storage ability of a powdered milk with vitamin C (see, for instance, Japanese Patent Laid-Open No. Hei 4-178349), a method of masking a fish oil with a lime flavor (see, for instance, Japanese Examined Patent Publication No. Sho 60-18382), a method of masking a fish oil with a yogurt flavor or milk flavor (see, for instance, Japanese Patent Laid-Open No. Hei 6-68), a method of blending a fish oil in a fermented milk (see, for instance, Japanese Patent Laid-Open No. Hei 6-90662), a method of blending a fish oil in ice cream (see, for instance, Japanese Patent Laid-Open No. Sho 63-216435) and the like.
In addition, besides those mentioned above, in order to improve the storage ability of a fish oil, there has been reported a method of suppressing oxidation deterioration comprising adding an antioxidant such as tocopherol or a tea extract (see, for instance, Gekkan Fudokemikaru (Monthly Issue Food Chemical), K.K. Shokuhin Kagaku Shinbun, 1990, 5, 54-60).
However, although various methods have been proposed as mentioned above, the generation of the taste of unpleasant fish odor cannot be satisfactorily suppressed in these methods.
For instance, there is a defect in the method of coating a fish oil with a protein hydrolysate and a milk solid content, the method of blending a fish oil in a powdered milk for infant rearing, and the method of wrapping a fish oil with cyclodextrin that the generation of an unpleasant odor is caused due to the oxidation of the polyvalent unsaturated fatty acid during storage.
In addition, as to the method of improving storage ability of a powdered milk with vitamin C, hardly any deodorizing effects can be expected. Also, in the method of masking a fish oil with a flavor, there is not only a defect that an unpleasant odor is felt after the intake, but also a defect that the application range to foodstuff is limited.
In the method of blending a fish oil in a fermented milk, there is a defect that since the fish odor is masked with an odor owned by the fermented milk, an unpleasant odor is felt after the intake.
In the method of blending a fish oil in ice cream, since the ice cream is subjected to frozen storage, the progress of the oxidation is suppressed to a certain extent, but some unpleasant odors are felt upon intake possibly due to the aggregation of the fish oil in the demulsification upon the preparation. Also, in the masking with a fermented milk, ice cream or the like, there is a defect that its application is limited.
Furthermore, in the method of adding tocopherol or a tea extract to a fish oil, hardly any deodorizing effects are obtained even when tocopherol is added at 0.1%. Also, if the tea extract is added in an amount of 0.1%, the oxidation degradation effects disappear in a short period of time, even though the oxidation degradation can be suppressed more than tocopherol, thereby showing elevation of peroxide value. Therefore, the effects are not satisfactory.
The present invention has been accomplished in view of the prior arts mentioned above. An object of the present invention is to provide a fat or oil composition which hardly generates an unpleasant odor or foreign taste even when a polyvalent unsaturated fatty acid such as DHA, DPA, EPA or ARA, an ester thereof or the like is formulated in foodstuff, and an oil-in-water droplet emulsion composition using the composition, and foodstuff containing these compositions.